Abstract
The electrochemical preparation of arrays of copper ultramicrowires (CuUWs) by using porous membranes as templates is critically revisited, with the goal of obtaining cheap but efficient substrates for surface enhanced Raman spectroscopy (SERS). The role of the materials used for the electrodeposition is examined, comparing membranes of anodized aluminum oxide (AAO) vs. track-etched polycarbonate (PC) as well as copper vs. glassy carbon (GC) as electrode material. A voltammetric study performed on bare electrodes and potentiostatic tests on membrane coated electrodes allowed the optimization of the deposition parameters. The final arrays of CuUWs were obtained by chemical etching of the template, with NaOH for AAO and CH2Cl2 for PC. After total etching of the template, SERS spectra were recorded on CuUWs using benzenethiol as SERS probe with known spectral features. The CuUW substrates displayed good SERS properties, providing enhancement factor in the 103–104 range. Finally, it was demonstrated that higher Raman enhancement can be achieved when CuUWs are decorated with silver nanostars, supporting the formation of SERS active hot-spots at the bimetallic interface.
Highlights
In order to find the best conditions for the electrochemical deposition of copper, preliminary analyses were performed by cyclic voltammetry in CuSO4 solutions, with
The reduction peak of Cu2+ to Cu0 was shifted to slightly more negative potentials on glassy carbon (GC) with respect to copper. This is because the deposition of copper on GC is more energy demanding than the deposition of copper on copper, the first process being affected by a the oxidation of both metallic coppertodeposited the cathodic branch higher overpotential because of thethe energy required form the during first metallic nuclei on a of the Cyclic voltammetry (CV)
This is because the deposition of copper on GC is more energy demanding than the deposition of copper on copper, the first process being affected by a higher overpotential because of the energy required to form the first metallic nuclei on a foreign substrate [52,53]
Summary
Recent years have seen increased interest in the development of miniaturized analytical sensors based on arrays of ultramicro- and nanowires [1,2,3] which, thanks to their microscopic structure, allow to achieve significantly improved analytical performances, especially as far as sensitivity and possibility of miniaturization are concerned [4,5,6]. It is worth reminding that a micro- or nanowire is defined as any cylindrical conductor with aspect ratio (i.e., length/diameter) ≥ 20 [7]. Numerous examples of novel sensors based on arrays of NWs or UWs, which exploit electrochemical or optical transduction, have been presented and reviewed [1,2,3,8,9,10]
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